Unidirectional exhalation valves are well known in the art. Generally, exhalation valves are check valves permitting air flow in one direction while preventing air flow in the opposite direction. The incorporation of an exhalation valve into a breathing device is necessary to enable the breathing mask to vent exhaled air from inside of the mask to the outside atmosphere, while preventing atmospheric air from being drawn back into the mask during inhalation.
Many exhalation valves are comprised on three basic parts, a hollow valve body that acts as both a valve seat and channel between the inside and outside of the mask, a flapper or disk valve and a valve cap, having vents or slots to permit air flow between the mask and the outside atmosphere.
An exhalation valve is positioned in the mask so that when the user inhales, the pressure inside of the mask goes negative. The negative pressure causes the flapper valve to be drawn against the valve seat thereby sealing the air passage through the valve body. When the user then exhales, the user's breath causes the pressure inside of the mask to go positive. The positive pressure and exhaled air, unseats the flapper valve, opening the air passage through the valve body and forcing the exhaled air out of the mask. An exhalation valve having a valve seat, flapper valve and valve cap is disclosed in Schneider, U.S. Pat. No. 3,085,591.
Because the pressure inside of the mask is changed only by the user's breathing, the cracking or break-open pressure of the valve must be relatively low yet maintain a proper seal to prevent back leakage. Flapper valves are usually made of resilient flexible materials such as rubber and are normally circular in shape to obtain a better seal on the valve seat. The circular shape of the flapper valve does, however, cause high exhalation resistance pressures. High exhalation resistance pressures can cause the user to become fatigued during the breathing cycle because the user must push harder with the lungs to overcome the resistance.
It is, thus, desirable to have an exhalation valve that seals tightly during inhalation to prevent back leakage into the mask, yet imposes very slight exhalation resistance pressures.
It is one object of this invention to provide an exhalation valve that has low exhalation resistance pressure yet provides excellent sealing characteristics to prevent back leakage.